( 69 ) 



Tlie solutions of tlie green clilorule <lo not however run further 

 than G, wliere the solution saturated with green also attains the 

 inner composition corresponding with the eciuilibriuin at the total 

 concentration. Solutions on GF could only be made by rapidly 

 dissolving a mixture of green and violet in the desired proportion 

 and then introducing some solid green chloride. These solutions 

 would then, however, recede towards (t as the point of linal equili- 

 brium of the liquid saturated with green chloride. 



The solutions saturated with violet chlorid run along the line EF. 

 The solution F might be at the same time in eqnilibrium with green 

 chloride, but as soon as this occurred the violet would be completely 

 converted into the green and then the solution containing the green 

 would again shift to G as a terminal point. 



As the line of eqnilibrium .4 ^7^ //intersects the solubility line for the 

 green but not that for the violet chloi'id, the latter cannot be definitely 

 in equilibrium at 25° with any solution, consequently at this tempe- 

 rature the green chloride is the only stable one. Even outside the 

 solution the violet changes, therefore, after a lapse of time, into the 

 green; iji contact with the solution this takes place more rapidly. 

 This is the reason why the line EF cannot always be followed np. 



The question now arises how it is possible to separate violet 

 chloride in the solid condition. This is done by leading gaseous HOI 

 into solutions containing at most 307o of green chloride and which 

 have been recently healed to 100^. 



Addition of HCl at 25° diminishes in a high degree the solubility 

 of both chlorides. 



The two lines DF and EF are shifted towards the left about 

 parallel to their original positions and about to the same extent. It 

 will be easily seen that the point of intersection G will also move 

 towards the left and might finally arrive in the liquid region to the left 

 of the equilibrium line. In that case (iiis line would no lono-er 

 intersect l)F but EF; a saturated solution of violet chloride would 

 then be in inner equilibrium and the violet chloride could be separated 

 in a stable condition. 



This, however, is not the case, because the line AG also moves 

 strongly towards the left on addition of HCl and consequently the 

 equilibrium in the solution shifts towards the green side. The investi- 

 gation showed that the violet chloi'ide is still metastable in contact 

 with the solutions rich in HCl; the point of intersection 7^^ therefore 

 remains, obviously, to the right of AIG even on additon of HCl. 



If, however, we heat to 100° before leading HCl, the line AIG 

 moves very considerably towards the violet side so that it now 



